Two rods A and B of different materials are welded together as shown in figure. Their thermal conductivities are K1 and K2. The thermal conductivity of the composite rod will be
From the diagram we can observe that both the rods are in parallel, then the total heat transfer will we be the sum of heat transfer from both the rods i.e.,
Htotal=HA+HB
As we know, H=KAΔtd
KtotalAtotalΔtd=K1A1Δtd+K2A2Δtd
Assuming, A1=A2=A
then, Atotal=A1+A2=2A
Ktotal2A=K1A+K2A
Ktotal=K1+K22